1. The Field of the Invention
The present invention relates to an endoprosthesis deliverable and deployable within a body vessel of a human or animal. More particularly, the invention relates to an endoprosthesis with improved visibility and/or crack and/or fatigue resistance capabilities.
2. The Relevant Technology
Stents, grafts, and a variety of other endoprostheses are well known and used in interventional procedures, such as for treating aneurysms, for lining or repairing vessel walls, for filtering or controlling fluid flow, and for expanding or scaffolding occluded or collapsed vessels. Such endoprostheses can be delivered and used in virtually any accessible body lumen of a human or animal, and can be deployed by any of a variety of recognized means. One recognized indication of endoprostheses, such as stents, is for the treatment of atherosclerotic stenosis, vulnerable plaque, dissections in blood vessels. For example, after a patient undergoes a percutaneous transluminal coronary angioplasty or similar interventional procedure a stent is often deployed at the treatment site to improve the results of the medical procedure and reduce the likelihood of restenosis. The stent is configured to scaffold or support the treated blood vessel; if desired, it can also be loaded with a beneficial agent so as to act as a delivery platform to reduce restenosis or the like.
An endoprosthesis is typically delivered by a catheter delivery system to a desired location or deployment site inside a body lumen of a vessel or other tubular organ. To facilitate such delivery, the endoprosthesis is typically capable of having a particularly small cross profile to access small diameter deployment sites. Additionally, the intended deployment site may be difficult to access by a physician and often involves traversing the delivery system through a tortuous luminal pathway. Thus, it can be desirable to provide the endoprosthesis with a sufficient degree of flexibility during delivery to allow advancement through the anatomy to the deployment site. Moreover, it may be desirable for the endoprosthesis to retain structural integrity during and/or after deployment and set.
Generally, an endoprosthesis can be constructed of multiple annular members or rings which are interconnected either through a connection section or a connection element. It is desirable for an endoprosthesis to have flexibility/stiffness properties to enable deployment through a tortuous luminal pathway yet have the stiffness properties which can be changed after deployment within a vessel. However, it can also be important for the endoprosthesis to retain its structural integrity after deployment by being configured to inhibit the formation and/or propagation of cracks as well as resist structural fatigue. Typically, flexibility can be controlled by the number and/or width of the rings and/or struts, the characteristics of the connection sections or elements, and/or the thickness of the material that forms the rings, the overall design of the endoprosthesis, material selection, length of the ring and or strut.
One problem with existing endoprosthesis designs relates to the difficulty in properly placing the endoprosthesis within a vessel prior to deployment of the endoprosthesis. Current endoprosthesis designs have thin struts which utilize less radiopaque material and therefore may not be as visible under fluoroscopy. An attempt to address the reduced radiopacity is to include radiopaque marker bands on the endoprosthesis, form the endoprosthesis of a radiopaque material or include marker bands on the delivery device. These marker bands may be located on the endoprosthesis to indicate an end of the endoprosthesis device, a length, a width, or the like. These marker bands have historically been soldered, welded, glued or press fit into hole features of the endoprosthesis device. A shortcoming of present designs is that the endoprosthesis are very difficult to manufacture, resulting in increased costs and manufacture time. Also, due to size limitations of the radiopaque material used, the markers may not provide sufficient visibility for precise placement.
Once deployed, the endoprosthesis can be capable of satisfying a variety of performance characteristics, as mentioned above. The endoprosthesis can be sufficiently rigid or provide an outwardly-oriented bias when deployed to perform its intended function, such as opening a lumen or supporting a vessel wall. Similarly, the endoprosthesis can have suitable flexibility along its length and/or width to inhibit any kinking or straightening that may occur during deployment or setting within a tortuous luminal pathway.
A significant failure mode in endoprostheses can occur as a result of crack formation and/or propagation through the body of an endoprosthesis. For example, failure can result from a stent element, such as a strut or elbow, beginning to crack during deployment, and subsequent propagation of the crack during setting and use. Such cracks can also initiate and/or propagate through the material of the endoprosthesis as a result of the cyclic loading that the stent undergoes during the pulsatile movement of blood and associated vessel expansion and contraction. For example, endoprosthetic fatigue failures can be encountered when nitinol stents are used in the superficial femoral artery (“SFA”).
Although various endoprostheses have been developed to address one or more of the aforementioned performance characteristics, there remains a need for a more versatile design that improves one or more performance characteristics without sacrificing the remaining characteristics.